The importance of etching aluminum and its alloys has increased significantly within the last several years. As the electronics industry has moved into production of very large scale integrated circuits (VLSI), the need for methodology which meets the requirements for their production has become increasingly acute.
The high-density, i.e. fine-line, geometries necessary for VLSI circuits make it essential that etching is anisotropic to achieve faithful delineation of patterns. It is well documented in the literature that anisotrophy is possible only where there is ion bombardment of the surface being etched. This does not mean, however, that etching will not take place if there is no ion bombardment.
The gases which must be utilized in the plasma etching of aluminum are highly reactive and form reactive species which are long-lived. The presence of these reactive species on side walls of etched steps will result in undercutting to some degree, depending on the lifetime of the species. This undercutting is a significant problem in VLSI production because of the need for anisotropic etching. A solution to this problem of undercutting is provided in accordance with this invention.